This invention relates to a photolithography system and process for manufacturing a semiconductor device. More particularly, this invention relates to a system for adjusting a photo-exposure time suitable for variable processing conditions in accordance with prior and following steps.
The greater a semiconductor device is integrated, the more line widths on the device must be narrowed. Furthermore, as the line width is reduced, more accurate alignment is required for patterns of stacked layers formed through a manufacturing process for the semiconductor device. Of all of the various pieces of equipment required for manufacturing semiconductor devices, a photo-exposure apparatus is the most important for determining the alignment accuracy for the stacked layers. In other words, in modern semiconductor manufacturing, a photo-exposure apparatus must have improved capacities for high resolution and fine alignment so as to be capable of manufacturing highly-integrated semiconductor devices.
Various techniques have been used for highly efficient photo-exposure apparatuses. For example, in order to enhance the alignment accuracy in semiconductor device manufacturing technology and to uniformly obtain a fine pattern in an accurate position, conventional G-Line light sources, with a wavelength of 436 nm, are gradually being replaced by I-Line light sources, with a wavelength of 365 nm, or deep ultra violet light sources, with a wavelength of 248 nm. Furthermore, a scanner-type source is dominantly being used rather than a stepper-type source.
There are several factors, such as a kind of lens system used or the light source used that influence the accuracy of a photo-exposure apparatus. In addition, an exposure time adjusting method, the kind and thickness of a photoresist material used, the baking conditions, the developing conditions, etc. may also effect the resultant quality of a photo-exposure work. In particular, a photo-exposure time is a very important parameter to finalize a line width and a uniformity of the pattern geometry. This is because photo-exposure time has an effect at the amount of a photochemical reaction of photoresist at an edge of a pattern image formed on a photoresist film.
Accordingly, although a line width of a pattern is primarily determined by the line width of a photo-exposure mask and a geometric optical configuration of a photo-exposure apparatus, a line width of a photoresist pattern may be also adjusted by controlling the photo-exposure time within a small range.
When controlling a photo-exposure time, it is necessary to first evaluate the size and quality of a photoresist pattern obtained from a previous photo-exposure time. Then, a photo-exposure time can be re-established by a kind of processing feedback according to this evaluation. In other words, an evaluation of a post-exposure step is fed back to a pre-exposure step, so that the pre-exposure step processing condition can be adjusted.
An example of the above technology is disclosed in U.S. Pat. No. 5,965,309. In this patent, a size and a shape of a resulting pattern obtained from a conventional patterning process using a photolithography and an etching are first evaluated. The evaluated result is then progressed, and a processing condition is re-established by means of a predetermined method to influence the patterning. In particular, a method is disclosed that is effective on a final pattern by adjusting a focus and an exposure rate in a photo-exposure process, in addition to the method of adjusting a condition in an etching process.
Although the above patent deals widely with techniques for conditioning photo-exposure and etching steps by adjusting patterning conditions through feedback, it does not clearly consider that a photo-exposure rate would be influenced by adjusting a photo-exposure time.
Meanwhile, a photoresist pattern obtained as a result of a photo-exposure work may be evaluated by an after-development inspection (ADI). Of course, the photoresist pattern is affected not only by various processing conditions directly related to a photo-exposure but also by a result of a pre-exposure step.
For example, if a film stacked before a photo-exposure process is made of a material having a characteristic of reflecting light well or preventing reflection, a photoresist pattern on the film is influenced by the preformed film. Certain parts of a photoresist pattern formed by a photo-exposure may be influenced by the topological pattern of a substrate surface, e.g., an uneven step coverage, formed before a photo-exposure process, or by a relative pattern position obtained after a photo-exposure process.
However, a current system for adjusting photo-exposure time cannot systematically apply a status of a result pattern or a pre-exposure step into the photo-exposure process. In addition, it has been problematic that a photoresist pattern position and a line width obtained after a photo-exposure process are variable based on the state of the power applied to a substrate.
Furthermore, in almost any manufacturing system it is necessary to periodically carry out data collection and evaluation in order use parameters obtained by a process evaluation result for the modification of a processing condition. However, it is not easy to maintain suitable processing condition in many cases while the data collection and evaluation are being carried out.